Linear tape drive systems provide for high-density recording on multiple tracks of a magnetic storage tape (the “tape”). In certain arrangements, parallel tracks extend along a longitudinal direction of the tape. During recording or playback, the read/write elements of the head should be aligned with the desired track as the tape moves in a longitudinal direction across the head. Closed loop positioners are often used in tape systems having higher track densities. In high-density tape systems, the tape may wander in the lateral direction (perpendicular to the longitudinal direction) as it moves in the longitudinal direction across the head, which can result in a positioning error or offset between the head and a center line of the desired track, also known as track misregistration (TMR). This type of off-track condition can be caused by a number of factors including tape dimensional stability (TDS) and/or dynamic tape skew. TDS is normally caused by changes in the operational temperature and/or relative humidity within the tape drive, which can cause changes the width of the tape. The ranges of temperature and humidity in the tape drive are fairly broad, i.e. temperatures of approximately 50-104° F., and relative humidity of approximately 10-80%. Thus, the dimensions of the tape changes as temperature and/or humidity vary within these ranges.
Tape cartridges for high-density tape drives are typically preformatted with information often called servo information, which is used to maintain the correct lateral position of the tape with respect to the head. Servo information provides the system with feedback to determine the continuous position of the tape relative to the head. Analysis of the servo signals allows for a determination of an offset and the distance of the offset between the track and the head. Based on the information, the head is moved by a positioner in the lateral direction to the center line of the track so that write/read operations can occur properly.
Linear Tape Open (“LTO”) is a computer storage magnetic tape format that employs a servo-based, closed loop control mechanism. The LTO roadmap calls for successive increases in capacity and speed, requiring increased track densities. As track densities increase with each new generation of LTO tape cartridges, the ability to precisely control the read/write head relative to the magnetic tape becomes increasingly important and more difficult, particularly due to phenomena such as tape dimensional stability and dynamic tape skew. These phenomena can cause not only lateral tape offset, but offset in other directions, such as an azimuth direction, particularly with such high track densities used in today's tape cartridges.